This application claims the benefit of Korean Application No. 2002-62295, filed Oct. 12, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a high frequency generator and, more particularly, to a noise filter of a high frequency generator.
2. Description of the Related Art
A high frequency generator, such as a magnetron, a klystron, a traveling wave tube and a semiconductor device, is applied in various fields. The high frequency generator mainly employs a noise filter to prevent undesired leakage of high frequency energy. The leakage of high frequency energy causes noise in electronic devices, such as a television and the like. For this reason, it is important to prevent leakage of high frequency energy from the high frequency generator. Generally, a noise filter includes inductive devices, such as choke coils, a capacitor, a shielding casing and the like, and are connected to an electric conductor to supply power.
FIGS. 1A and 1B are partially sectional and top views of a conventional noise filter of a high frequency generator, respectively. FIGS. 1A and 1B are also shown in Korean Non-examined Patent Publication No. 10-1999-0072650. As shown in FIGS. 1A and 1B, a noise filter 120 is disposed under a magnetron 100. Inside a filter casing 144 of the noise filter 120, choke coils 154, each including a core inductor 150 and an air-core inductor 152 connected in series to each other, are disposed. The core inductors 150 have high frequency-energy absorbing members 148 inserted thereinto, while the air-core inductors 152 do not have the high frequency-energy absorbing members 148 therein. The core inductors 150 are connected to a condenser 158. The air-core inductors 152 are connected to a stem 156 through stem terminals 156a and 156b. 
Generally, a core inductor may reduce noise of a frequency band below 400 MHz by regulating a number of coil windings thereof. An air-core inductor may reduce noise of a frequency band ranging from 700 MHz to 1000 MHz by regulating a number of coil windings thereof. In the conventional noise filter shown in FIGS. 1A and 1B, the core inductors 150 and the air-core inductors 152 are connected in series to each other, and sectional areas of the high frequency-energy absorbing members 148 are sized, so noise of a frequency band ranging from 400 MHz to 700 MHz is reduced.
However, although a noise frequency band causing many communication obstacles ranges from 400 MHz to 900 MHz, the conventional noise filter may not reduce noise of a frequency band ranging from 400 MHz to 900 MHz using the core inductors 150, the air-core inductors 152, or a structure in which the core inductor 150 and the air-core inductor 152 are connected in series to each other.
Accordingly, it is an aspect of the present invention to provide a noise filter of a high frequency generator, which may reduce noise of a certain frequency band leaked from the high frequency generator using a structure in which a core inductor, an air-core inductor and another core inductor are connected in series to each other.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
The foregoing and/or other aspects of the present invention are achieved by providing a noise filter of a high frequency generator having a structure in which a first core inductor, an air-core inductor and a second core inductor are connected in series to each other. The first and second core inductors have high frequency-energy absorbing members inserted thereinto, and the air-core inductor is not provided with a high frequency-energy absorbing member.
According to an aspect of the invention, the high frequency-energy absorbing member is made of one of iron oxide, tin alloy and ferrite.
According to another aspect of the invention, the high frequency-energy absorbing member is provided with a sectional area in which noise of a frequency band ranging from 400 MHZ to 900 MHz is attenuated.